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R. A. FES'SENDEN.

WIRELESS DIRECTION FINDER. APPLICATION FILED JULY 28, me

1,37%;293. I Patented Apr. 12, 1921.

W I TNESS:

I N VEN TOR.

20 of errors in estimating direction due to the UNITED A ES-PAT NT OFFICE...

REGINALD A. FESSENDI iN, OF -.CH1559:1911"! HILL, SSAOHUSETTS.

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To all whom it may concern:

Be it known that I, REGINALD DEN, of Chestnut Hill dlesex and State of 'A. Fnssnnin the county of Mid- Massachusetts, a c tizen 5 of the United-States, have invented nave-and ,useful Improvements in Wireless Directiom Finders, of which the following is thespeci- My invention relates to means for deter- -mining direction by electro-magnetic wa'ves,

bending of the electro-magnetic waves around conducting obstacles, or in the neighborhood of bodies of different conductivities.

Figures 1 and 2 show, partly diagrammatically, apparatus suitable for carrying out my invention, and illustrating the Dolbear, Edison, and Tesla.

method of its operation.

vIn the practice of wireless telegraphy it has been heretofore, and still is, generally the custom to utilize the electrostatic component of Hertzian waves by means of vert1- cal antennae, of the type first proposed by Applicant in 1899 made the discovery that the electromagnetic component could be. utilized by means of vertical coils of wire with or without magnetic cores, and published this discovery, (Electrical World, An ust 12, 1899).

everal years later applicant discovered that these loops for utilizing the magnetic component We're peculiarly well adapted for determining the direction of the source of received wireless signals, either by mounting the loops on a rotating stand as shown in U. S. application Serial No. 167,242, filed:

July 27, 1903; issued in part as U. S. Patent No. 1,020,032. Also German Patent 225,256,.

or by arranging a number of them radially and connecting .them to a commutator as shown in U. S. applicatlon No. 352,213, filed January 14. 1907, the corresponding French patent being No. 385,897, and the corresponding German Patent No. 225,256. Also i ihciicatton oflettersl'atent.

, tive connection.

' ground.

Batented Apr. 12, 1921.

Application filed raiy 255919."- seiau mi. 818,726.

ma No. 7 54,058. The modification subsequently made by Bellini and Tosi, (British patent specification No. 21,299 September 25, 1907) consisted in modifying applicants loop 'U./ S application Serial. No. 168,800 filed, -August 8, 1903, and issued as U. S.

method In substituting an inductive connection in p ace of applicants original conduc- Applicant termed this type of direction finder discovered by him, a pelorus, because it gives the direction of the source of electromagnetic waves relative to the lubber line of the ship, and has no relation whatever to the points of the compass.

The first experiments made with this type of apparatus in the years 1899-1901 were made over distances not exceeding twenty miles, and gave quite accurate results, and the apparatus was demonstrated and tendered to the U. S. NavyI (letter to U. S. Bureau of Equipment, avy Department,

.Was'hington, D. (3., July 8, 1905 also London "Electfician, February 22, 1907), but though the Navy Department was interested, at the time there was no demand for apparatus of this character.

' Later experiments, 1901-1906, made over distances exceeding one hundred miles, showed that the method frequently gave results in error byas much as twenty degrees from the true direction, and in later tests,

1906-1907, errors of as much as forty-five degrees were sometimes observed.- As the result of numerous experiments, applicant discovered the causes of these erroneous readings and invented a new type of wireless !direction finder.

The cause was found to be the existence of regions more or less opaque to the travel of the electromagnetic waves, thereby causing the production of shadows, and the bending of the direction of travel of the electromagnetic waves" around the edges of the opaque regions.

Over land these opaque regions were found to be due tog Varying local conductivity of the Certain sections of the land surface appear to form insulated pockets. exists for example just outside'of the city of Pittsfield, where the street railway could not operate its system in 1891 untiLMr. C. C. Chesney discovered the trouble to be due to Such a pocket the extremely high resistance of the ound return. This pocket appears to be ormed' of insulating rock strata which come tg this o-w surface and form a sort of'insulating filled with conducting soil, this con ucting soil, however, being msulated from the ex? terior country by the edgesof the insulating'bowl. 1 a

A similar insulating bowl was described by Dr. Kennelly in the London Electrio-ion, at one ofthe cable landings inthe Canadian Maritime Provinces. V

b. Varying. local and temporal absorption due to vegetation; p H

As pointed out by applicant in 1903, every tree acts as an antenna, and absorbs; energy, and the amount of energy absorbed depends on the amount of sap 1n the trees '(Ele'at'rz'cal W orld and Engineer, November 14,

Over water and parallel to a coastline,

' such as that between Cape Henry and Cape beach, causing Hatteras, the error in directionwas found to be due toc. The "reat diiference between the resistance of tlie'water andthat of the sandy the electromagnetic waves to bendin. J Y

Over the sea, and also over the land, directional errors were also found to be due to the presence of the large bodies of ionized air, discovered by applicant through his transatlantic experiments to exist in the upper regions 0 the atmosphere, and described by him in the Electrical Review, March 1148,1906.

The new type -of direction finder (USS.

application Serial No. 356,814, filed Feb. 11,

1907, corresponding British Patent "*No.

2955/1908) was based. on the application'of horizontal electromagnetic waves instead. of

vertical waves, and was found to give in practice considerably more accurateresults up to the limit of its range. Its range was, however, shorter than that ot'the original Fessenden pelorus, using vertical Waves.

Applicauts present invention is a modification and an improvement of the original vertical wa've Fessenden pelorus, and is based upon applicantsdiscovery that the amount of the bending, .i, ,e., the amount of directional error, is a function of'tlie wave length of the electrpmagnetic waves used for direction finding. In applicanfisnew method, instead of a single frequency of electromagnetic waves, two, and preferably three, frequencies are used, and .by m'eans of th readings obtained withthese different frequencies of transmission the existenceiof an error is detected and its amount may" be estimated with a fair degree of accuracy. I

Fig. 2 illustrates the use of the method. Here 65 is a wireless station arranged'to emit signals of a plurality of frequencies,

rectional readin for example, 200,000 per second and 100,000

' per second' 52 IS a vessel equipped with a Fessenden pelorus of the type shown in 'parallel with the coast, their path of travel 'is inclined as mentioned previously in the specification, and the dotted lines 53--5557 may betakento represent-the paths of travel of'the waves having a fre uency of 200,000

'per second, and the lines 0 small circles 54, 56,"58, the paths 'of the waves of frequency of 100,000 per second.

The observer on the vessel 52 observes the direction as given by pelorus, with the prelorus arranged to receive waves of 200,000

(fluency. I e then takes a second reading with the i elorus arranged to receive waves of 100,000

re uency. fl both these readings give the same di' rection, the observer. knows that there has been no bending of the paths of either of the two frequencies of electromagnetic waves,and that the direction is a true one. If, however, there is a difference in the readings for the two frequencies he knows that the path of the waves has been bent and'by certain formulae which do not form a part of this invention and are therefore not herein given, or still more simply, by empirically observing what differences in the directional readin for the two fre uencies correspond to a given angle of bent ing, he can determine the true direct-ion. V While the use of two frequencies is shown it is preferred to use also a third frequency the arrangement for receiving which is s own in Fig. 1, because by using three fre uen'cies comparisons m be made between t ree airs of frequenci s, and the results obtaine with each air may be used as a check onthe results 0 tained with the other pairs.

Fig. 2 also shows, in its lower section, the effect of a large cloud of ionized air 62. 'Here the vessel 64 will obtain the same dion both frequencies, because the path s own by the dotted lin'e .of the waves of frequency 200,000 will be the. same as the path (shown by the line of circles '61) of the waves of frequency passing I amount of' bending, as applicant has (llSCOVuTQCl from his experiments, varies wi'h the wave length, the paths of 60 and 61 will diver e after passing aroundthe edge of 62, and t 1e readings obtalned with the pelorus on the vessel 63 will be different for the different frequencies as. to direction; and will also differ in intensity, which latter phenomenon ma also be made use of as a check.

pparatus suitable for carrying out the invention is shown in Fig. 1, where88 is a large disk formed of woodor papier mach on which'is wound the magnetic component receiving coil 74, as described in U. S. a plication Serial No. 167,242, filed July 2% 19,03, and U. s. Patent No..754,058, filed August 8, 1903, and German Patent No. 225,256, filed January 8, 1907.

72, 73, are wire supports for the spool 88,

and 83, 84 are insulators to which 72, 73'

are attached as shown, and 81 82, are, supports of the revolving turn table 85, 86 being the fixed base.

89, 91 are tunin capacities whereby the coil 74'may be tune to any one of three desired frequencies by leaving both of the ke s 88,: 90 open, or closing the key 88, or cosmgboth 88 and 90.

It will be obvious that the use of appliicantselorus without means for discoverresult in large errors in navigation. As an illustration, it is understood that on one ocdescribed above, which were disclosed to the U. S. Army and Navy Departments in December, 1914, but have been kept secret until now, these difiiculties are largely overcome.

What I claim. is

In the art of direction finding, the method of determining the direction of asource of I radiant energy from an observing station, 8 is a receiver of any suitable type, and 87', 1

which consists in taking a plurality of 0bservationsat the observing station, at dif- -fe'rent wave frequencies of the energy emitted from the radiant station, of the direction of the waves received from said radiant station, and from the amount of the discrepancy between said observations, de-

termining the amount of bending, of said waves and the true direction of the radiant station.

I REGINALD A. FESSENDEN. 

